It appears the orientation of the bulb has an influence on how far the stem will travel. I'm kind of surprised that more stem bulblets didn't form on the grand example at the lower right. This picture is an excellent illustration of the individual feeder root character variations from bulb to bulb within the species. Edit added: Individual variation within the species, etc. I'll bet the heavy ground feeder on the left was a fine example of the plant. Important photo.
